The present invention relates to scintillator compositions and related devices and methods. More specifically, the present invention relates to scintillator compositions including a scintillation compound and a dopant for use, for example, in radiation detection, including gamma-ray spectroscopy, and X-ray emission and neutron detection.
Scintillation spectrometers are widely used in detection and spectroscopy of energetic photons (e.g., X-rays and gamma-rays). Such detectors are commonly used, for example, in nuclear and particle physics research, medical imaging, diffraction, non destructive testing, nuclear treaty verification and safeguards, nuclear non-proliferation monitoring, and geological exploration.
Some commonly used scintillator materials include thallium-activated sodium iodide (NaI(Tl)), bismuth germanate (BGO), cerium-doped gadolinium orthosilicate (GSO), and cerium-doped lutetium orthosilicate (LSO). While these known scintillator materials do have some desirable scintillation characteristics which make them suitable for certain applications, each of the materials possesses one or more deficiencies that limit their use in a variety of applications. For example, many currently available scintillation materials have low light output characteristics, poor timing resolution (e.g., slow decay time or rise time), or low X-ray or gamma-ray stopping power. Some available materials also have emission spectra not optimally matched for use with certain commonly available photodetectors or have limited temperature ranges at which scintillation is practical or possible. In some instances, utility of certain available scintillators is limited due, for example, to absorption of oxygen and moisture leading to persistent afterglow and high background rate due to radioactive isotope of component elements.
Some important requirements for the scintillation materials include, for example, high light output, transparency to the light it produces, high stopping efficiency, fast response, good proportionality, low cost, and availability in large volume. For certain applications, sensitivity to neutrons is needed. These requirements on the whole cannot be met by any of the commercially available scintillators. While general classes of chemical compositions may be identified as potentially having some attractive scintillation characteristic(s), specific compositions/formulations having both scintillation characteristics and physical properties necessary for actual use in scintillation spectrometers and various practical applications have proven difficult to predict. Specific scintillation properties are not necessarily predictable from chemical composition alone, and preparing effective scintillators from even candidate materials often proves difficult.
Energy resolution is one important characteristic influencing utility of a particular scintillator composition, with energy resolution being affected by factors such as light output and linearity of response. Larger light output also allows for easier crystal determination in scanners that use discrete crystal arrays. Good energy resolution makes it possible to separate photopeak events from those in which the photon has scattered in the patient, making energy resolution very important for applications such as 3-D whole body positron emission tomography (PET). Better crystal determination leads to improved scanner spatial resolution. The sensitivity of the scanner is determined by the effective Z and density of the crystal. The effective Z of the crystal affects the fraction of photons that Compton scatter in the crystal, rather than depositing all their energy in a photoelectric interaction. Scanners which use low Z crystals have poorer spatial resolution, as photons may produce a Compton electron in one crystal and a photoelectric interaction in another. The stopping power is directly proportional to crystal density, and is also somewhat dependent upon the crystal's effective Z. Finally, the decay time of the scintillator is important for several reasons. First, the faster photons are emitted by the scintillator, the better the scanner timing resolution will be. The position uncertainty along the LOR in an event is proportional to cΔt/2, and TOF-PET reconstruction algorithms can take advantage of this to improve the signal to noise ratio in the reconstructed image. Second, the longer the scintillator emits light, the longer the dead time between pulses. This is particularly a problem for pixelated detectors which utilize light sharing among multiple PMTs to determine which crystal absorbed the 511 keV photon. Thus, the search for new scintillators that are proportional, have higher light outputs, faster decay times, and higher densities than currently available scintillators is an active field of research.
As a result, there is continued interest in new scintillator compositions and formulations with both the enhanced performance and the physical characteristics needed for use in various applications. Today, the development of new scintillator compositions continues to be as much an art as a science, since the composition of a given material does not necessarily determine its properties as a scintillator, which are strongly influenced by the history (e.g., fabrication process) of the material as it is formed. While it may be possible to reject a potential scintillator for a specific application based solely on composition, it is typically difficult to predict whether even a material with a promising composition can be used to produce a useful scintillator with the desired properties.
Thus, a need exists for improved scintillator compositions suitable for use in radiation detection applications.